The present invention relates to an implanted tissue stimulator system and catheters and more specifically for use in the intrathecal space.
The concept of using electronic stimulation systems for the purpose of controlling nerves or muscles is well known. These systems typically utilize an implantable or an external pulse generator. The external systems consist of a transmitter and antenna which transmits energy and/or stimulation signals transcutaneously through a patient's skin to an implanted receiver. The receiver provides signal processing of the received pulses and transmits the energy derived therefrom to activate electrodes implanted adjacent to specific types of tissue to be stimulated. A system like the one described above has been disclosed previously in U.S. Pat. No. 3,727,616. It is also known in prior art where more than one pair of electrodes are activated such as U.S. Pat. No. 3,449,768.
Problems arise in these prior art systems where electrode placement fails to provide the desired physical response. It may also occur later if a change in patient condition or electrode position occurs. This failure may also be caused by improper polarity of the stimulated electrodes relative to one another. Furthermore, it is often required that the electrodes be implanted surgically adjacent to one or more nerve fibers. This type of procedure involves inherent risks due to the fact that it is often performed in close proximity to the brain or spinal cord or other sensitive nerves or tissues. It is therefore desirable to perform the electrode implantation only once to minimize the surgical risks to the patient as well as the financial burdens. Moreover, even when a plurality of electrodes have been utilized, such that repeated surgical procedures are not required, the prior art systems did not provide for dynamic programming and reprogramming of different electrodes after surgery until U.S. Pat. No. 4,459,989 to Borkan.
The Borkan patent '989 disclosed an external stimulator system which allowed noninvasive programming of the stimulated electrodes. Each electrode was capable of assuming a positive, negative or open circuit status with respect to the other electrodes. This effectively allowed the electrodes to be “repositioned” non-invasively. That same programming ability (plus/minus/off) was later applied to totally implantable systems as well. The system had mono/biphasic control also. Further improvements are described in U.S. Pat. No. 4,612,934 also to Borkan.
The application of spinal cord stimulation has shown itself to be effective in the treatment of pain and is under study for various other medical conditions. Initially, the leads were implanted by laminectomy and applied to the dura in the epidural space. The next generation of electrodes were positioned by percutaneous implantation. These were either placed into the intrathecal space or the epidural space. Due to the construction and nature of the electrodes used at that time (approximately 30 years ago), numerous complications occurred with the use of intrathecal catheter electrodes. These included CSF leakage. In addition, intrathecal electrodes were prone to significant movement and migration (as were the early epidural leads).
Therefore, development efforts were focused on percutaneous implantations in the epidural space. An example of a multielectrode catheter assembly for spinal cord stimulation is shown in U.S. Pat. No. 4,379,462 to Borkan.
Advances in catheter technology have allowed the widespread application of intrathecal catheters that deliver drugs for various medical applications. In addition, various fixation means for catheters have been developed and successfully utilized to eliminate the problem of electrode movement and migration. Therefore, it is now possible to develop a catheter electrode for placement into the intrathecal space without the problems and complications experienced previously.
The recent use of totally implantable stimulator systems with an implanted power source have resulted in increased emphasis on the amount of power required to deliver an effective stimulation regimen. In addition, use of multielectrode systems has put an even greater strain on the limited resources of an implanted power cell.
The intrathecal space provides a more direct means of delivering either drugs or electrical stimulation to the spinal cord. By definition, implantation of devices in the epidural space place stimulation or drugs outside the dura, significantly further away from the spinal cord. Intrathecal placement therefore allows significantly reduced levels of stimulation and drugs to create the same effect as a catheter placed epidurally.
Various stimulation catheters are disclosed to lie along and stimulate tissue in the intrathecal space. The electrodes on the leads are various sizes to conserve the battery as well as allowing a more defined area of stimulation. It may also include multiple channels or passages for delivery of drugs, thermal or photonic energy. The sheath includes a fixing element configured to fix the electrode in place along the tissue.
One embodiment of the intrathecal stimulation lead includes a sheath having at least one electrode along the exterior of a distal end of the sheath to lie in-line along the tissue. The fixing element may include at least one of the following: inflatable balloons, nitinol, tines and the sheath shape.
The sheath also include a passage extending from an inlet at the proximal end of the sheath to one or more outlets at the distal end of the sheath. The outlets may be located at one or more locations including, but not limited to, the area between the electrodes and on the electrodes. This passage may be used for dispensing of drugs. It may also be an optical channel or for a stilet to be used during positioning of the lead. This may be used without fixing elements.
Alternatively, one or more optical channels can be provided extending from a port at the proximal end of the sheath to a port at the distal end of the sheath. The port for the optical channel at the distal end may be located at one or more of the tip of the distal end, the area between the electrodes and on the electrodes. The optical channel can provide photonic energy to the tissue as well as functioning as a lens for a remote camera. The passage which extends from the inlet of the proximal end of the sheath to one or more outlets at the distal end of the sheath may be used with at least one electrode along the exterior of the sheath to lie along the tissue to be stimulated. The same passage (or another) may also allow the use of a stilet during positioning of the lead.
In one embodiment, the electrodes extend no greater than 270° about the exterior of the sheath. The leads can extend anywhere in the range of 30°–270°. This reduces the surface area of the electrodes and therefore the power required by the battery. It also allows the electrodes to have a more defined or localized stimulation. Wherein the electrodes extend less than 360° about the exterior of the sheath, the length of the each electrode along the sheath should be typically at least three millimeters. If the electrodes extends 360° about the sheath, the length of the electrodes along the sheath typically would be three millimeters or less. The currently preferred length is two to four millimeters.
In another embodiment, an additional electrode spaced along the length of the sheath from at least three in-line electrodes at the distal end of the sheath. By positioning the additional lead on the sheath it is closer to the distal electrodes and thereby reduces the current path compared to using the stimulator casing as the additional lead in a monopolar mode. The additional electrode has a surface area on the sheath greater than the surface area on the sheath of each the at least three electrodes. The additional electrode is typically at least twice the surface of the at least three electrodes and may be spaced, for example, at least 10 millimeters from the other electrodes. The increase in surface area can be by varying the length along the sheath or diminishing the circumference around the sheath of the electrodes. The lead may be activated in either a bipolar mode using two of the at least three electrodes and in a monopolar mode using the additional electrode as a common anode and at least one of the other electrodes as a cathode.
A method of neurostimulation according to the invention includes inserting a catheter electrode assembly into the intrathecal space and positioning it adjacent to the spinal cord. The catheter electrode includes a sheath having a distal and proximal end and at least three in-line electrodes along the exterior as well as a fixing element to fix the electrode in place along the spinal cord. The electrodes are fixed at a desired location along the spinal cord using the fixing element. The stimulation pulses are provided to one or more of the electrodes. Where the catheter includes a passage with one or more ports at the distal end of the catheter, the method further includes administering a drug through the passage.
The invention also anticipates an embodiment wherein the electrodes extend no greater than 60° about the exterior of the sheath, the electrodes are positioned along the nerve root where it enters the spinal cord (dorsal root entry zone). Alternatively, where the electrodes extend no greater than 90° about the exterior of the sheath, the electrodes may be positioned along the midline of the spinal cord to stimulate only the longitudinal and not the bending nerve fibers.
The catheter of the present invention can also be used for a drug treatment method. This method includes positioning a stimulation catheter adjacent to the tissue to be treated by the drug and administering a drug to the patient via the catheter. The tissue is then stimulated using the catheter. The catheter may include one or more contacts at the distal end if the catheter stimulation is by electric energy. As an alternative or in combination, an optical channel with one or more ports at the distal end of the catheter would provide stimulation by photonic energy. Alternatively, drugs may be administered systematically or concurrently with intrathecally administered agents.
The drug administered may be selected to be responsive to stimulation. Wherein the drug is responsive to light energy with a specific wavelength, the stimulation of the tissue is with the light energy of that specific wavelength using the catheter. Wherein the drug is responsive to heat or cold, the tissue is stimulated with heat or cold using the catheter. The heat may be produced by electrical energy or photonic energy. The cold may be produced by a Peltier effect device or other means for example gas or liquids. An additional optical channel with a port at the distal end of the catheter may be provided and is used to position the optical channel.
Finally, intrathecal stimulation by light energy may be administered via the catheter—with or without drugs or electrical stimulation—to activate certain tissues. These tissues may, in some cases, be treated in some manner to increase their sensitivity to this method of activation and maybe used in combination with electrical stimulation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.